The present invention relates to a hydraulic brake booster for a vehicular brake system, which is actuated by means of a brake pedal. The brake booster includes a travel limiting spring and a control valve which controls both the interconnection of a storage source with a booster cylinder and the interconnection of the booster cylinder, which contains a booster piston, with a relief station. The brake booster is connected to a hydraulic dual-circuit main cylinder having a primary and secondary side sealed from each other by a double piston.
A similar brake booster is disclosed in German Pat. No. 2,001,483, issued July 30, 1970. With brake boosters of this type, a problem exists in that the hydraulic supply of the main cylinder refill container can be depleted after repeated lockage avoidance operations. It is well known that, in order to prevent this problem, a special return pump is used which conveys the brake pressure medium drawn off by the wheel brake cylinders back to the main cylinder, see British Pat. No. 1,416,645, issued Dec. 3, 1975. Such a return pump is, however, cumbersome and costly.